The present disclosure relates to an image forming apparatus developing an electrostatic latent image by using a magnetic toner.
In an image forming apparatus using a magnetic toner for development of an electrostatic latent image, if an amount of a magnetic toner in a development device is small, an amount of the magnetic toner supplied to the electrostatic latent image becomes insufficient and an image is blurred. On the other hand, if the amount of the magnetic toner in the development device is large, when the magnetic toner is agitated and the magnetic toner is charged, electro static charge of the magnetic toner becomes insufficient. Either case causes degradation of image quality. Therefore, by utilizing a magnetic sensor, the amount of the magnetic toner in the development device is controlled by the predetermined value.
In a technique suggested as an example of controlling the amount of the magnetic toner in the development device, the magnetic toner is replenished to the development device continuously for a predetermined time before controlling image density. In accordance with an output value of the magnetic sensor before the replenished magnetic toner reaches the magnetic sensor and an output value of the magnetic sensor when the supplied magnetic toner reaches the magnetic sensor, a correcting time to a predetermined toner replenishing time is determined.
However, even if the magnetic sensors are the same product, dispersion of the output values inevitably occurs according to individual products. Therefore, if the amount of the magnetic toner in the development device is controlled by utilizing that the amount of the magnetic toner in the development device becomes a predetermined setting value when the output value outputted from the magnetic sensor is a predetermined value, it is necessary to adjust the output value for each magnetic sensor.
For the magnetic sensor, there are various manners. Among these, a differential transformer-type magnetic sensor is a permeability detecting-type sensor and comprises a drive coil, a detection coil and a standard coil. In a case of the differential transformer-type magnetic sensor having a structure that the drive coil, detection coil and standard coil are arranged in a core, it is possible to adjust the output value by adjusting a position of the core.
On the other hand, in a case of the differential transformer-type magnetic sensor having a structure that the drive coil, detection coil and standard coil as a plane coil are formed on a print substrate, the core is not provided, and therefore, it is regarded that the output value is adjusted by using an amplifier.
In both case, it is necessary to adjust the output value for each magnetic sensor, and accordingly, trouble occurs.